1. Field of the Invention
The present invention relates to the technical field of X-ray shielding, and particularly to the protection of humans, such as X-ray technicians and equipment operators, from the effects of exposure to radiation damage.
2. Background of the Invention
Medical workers and others who work with X-rays and X-ray equipment require protection from the radiation. Long term exposure, even to very low levels of X-rays, is known to produce a substantial number of serious effects.
Such workers are normally furnished with protective garments, including coats, aprons, gloves, thyroid shields, gonad shields, and the like.
Protective garments or coverings are increasingly being employed to protect medical patients from excessive and stray X-ray exposure. Protective garments may be in the same form as those employed by technicians. Other protective coverings may include sheets, drapes,
Such protective garments are made most commonly from rubber sheets filled with lead, lead oxide, or other lead salts, or from laminates of lead foil faced with polymer films. Natural rubber is frequently employed, but other synthetic rubber may also be employed, such as styrene-butadiene (SBR), polyisoprene, polybutadiene, and the like, as well as polyolefins, such as polyethylene, or polyesters, such as polyethylene terephthalate are employed as well.
So that the relative protective value of shielding materials can be assessed and compared, it is common to relate the attenuation of incident X-rays to the attenuation of elemental lead foil. Standard levels of protection for X-ray shielding are 0.5 mm of lead and 0.25 mm of lead, and equivalents to these attenuation valves or better must be attained in other forms of materials. Thus, attenuation is normally expressed as mm of lead equivalence.
The forms of shielding materials heretofore employed are quite heavy, resulting in cumbersome, hot, uncomfortable, and inconvenient garments and the like which often hinder the wearer. In addition, the materials are not durable because of the very high loadings of the filler materials into the rubber sheet or the eventual breakdown of lead foils, after repeated flexing. In addition, the materials are relatively difficult to fabricate into useful garment forms.
Barium salts, and particularly barium sulfate, are extensively used as a contrast medium for diagnostic X-rays and have long been known to be opaque to such radiation. Such salts have been incorporated into surgical materials such as sponges, sutures, and the like for post-operative detection. See, for example, U.S. Pat. No. 4,185,626. Barium sulfate is also employed as a base material for X-ray fluorescent recording film.
Barium salts, and barium sulfate in particular, have not been employed in X-ray shielding films because the volume required to achieve acceptable levels of shielding require either unacceptably thick and expensive sheets or loadings in rubber films at proportions which unacceptably compromise the mechanical properties, and particularly the flexural modulus and resistance to flexing.
While barium and barium salts have often been incorporated into polymer systems for a wide variety of purposes, the levels acceptable rarely exceed about 40 weight percent, although occasional applications at levels up to about 50 percent are known. Higher loadings are required to afford useful X-ray shielding in sheet materials of workable thicknesses.